The entire disclosure of Japanese Patent Applications Nos. 2000-289889 filed on Sep. 25, 2000, 2001-100989 filed on Mar. 30, 2001 and 2001-280095 filed on Sep. 14, 2001 including specification, drawings and abstract is herein by reference in its entirety.
1. Field of the Invention
The invention relates to a hydraulic bearing device that supports a rotating shaft or the like.
2. Description of the Related Art
FIG. 1 shows three partially developments of inner surfaces of bearing metals which constitute radial hydraulic bearing devices according to the related arts. Plural hydrostatic pockets 1, 2 that are quadrilateral grooves such as shown by FIGS. 1(A) and 1(C) or U-shaped grooves such as shown by FIG. 1(B) are formed on inner surface of the bearing metals along a rotational direction of a rotating shaft. An oil-supplying hole 3 is formed in each hydrostatic pocket. Inner surface of the bearing metal except the hydrostatic pockets are land portions 4 for generating hydrodynamic pressure. FIG. 2 shows three plane views of bearing metals which constitute thrust hydraulic bearing devices according to the related arts. A hydrostatic pocket 5 that is a ring shape groove such as shown by FIG. 2(A) or plural hydrostatic pockets 6 that are partially ring-shape grooves such as shown by FIGS. 2(B) and 2(C) are formed on a surface of the bearing metals. Plural oil-supplying holes 3 are formed in the ring shape hydrostatic pocket 5, and a oil-supplying hole 3 is formed in the each partly ring shape hydrostatic pocket 6. The surface of the bearing metal except the hydrostatic pockets 5, 6 are land portions 4 for generating hydrodynamic pressure. Here, hydraulic bearing devices are distinguished two types that are a separated type such as shown by FIG. 1(C) or FIG. 2(C), and a non-separated type such as shown by FIGS. 1(A), 1(B) or FIGS. 2(A), 2(B) according to a shape of the land portion 4. The land portion 4 of the non-separated type is continuously all around of the surface of the bearing metal. On the other hand, the land portions 4 of the separated type are separated to rotational direction by drain grooves 7 that are formed between each hydrostatic pocket. At aforementioned hydraulic bearings, when pressure adjusted lubricant oil is supplied to the hydrostatic pockets 1, 2, 5, 6 through the oil-supplying hole 3, the hydraulic bearing functions as a hydrostatic bearing by filled lubricant oil between the hydrostatic pockets 1, 2, 5, 6 of the bearing metal and an outer surface of a rotating shaft. Simultaneously, since the lubricant oil is filled between the land portion 4 and the rotating shaft, when the rotating shaft is rotated for the bearing metal, the hydraulic bearing functions as a hydrodynamic bearing by wedge effect that is generated between the land portions 4 and the outer surface of the rotating shaft.
Then, at the non-separated type bearing, especially in a case of U-shaped hydrostatic pockets 2 such as shown by FIG. 1(B), since area of the land portion 4 is large and continuously, a large amount of hydrodynamic pressure is generated. Therefore, the non-separated type bearing is effective in high rigidity and high damping effect. However, in a case of high rotating speed, a great heat due to fluid friction is generated at the land portion 4. The great heat causes thermal expansion of the bearing metal, and a clearance between the bearing metal and the rotating shaft decreases. As the result, calorific value by fluid friction increases, and thermal expansion of the bearing metal increases. This is in a vicious circle that causes to deteriorate the performance of the bearing.
On the other hand, at the separated type bearing, heat generating at the land portion 4 is restrained because it is easy to be drained the lubricant oil by existence of the drain grooves 7. However, existence of the drain grooves 7 causes deterioration of the rigidity because the land portion 4 is separated and small. Moreover, the separated type bearing tends to cause cavitation.
It is an object of the present invention to provide an improved hydraulic bearing device.
A hydraulic bearing device that supports a rotating shaft comprises a bearing metal. On a surface of the bearing metal, a hydrostatic pocket and a land portion are formed. The land portion is defined by the hydrostatic pocket and generates hydrodynamic pressure. The hydraulic bearing device further comprises a pressure fluid supplying source and an oil-supplying hole. The oil-supplying hole is opened in the hydrostatic pocket and provides pressure fluid from the pressure fluid supplying source to the hydrostatic pocket. On the land portion, a drain hole that drains the fluid is formed.
Because the hydraulic bearing device is provided with the hydrostatic pocket and the land portion, it functions not only as a hydrostatic bearing but also as a hydrodynamic bearing. Then, since the fluid is drained through the drain hole, thermal expansion of the bearing metal due to heat generation of the fluid is restrained. Moreover, since the drain hole does not separate the land portion, deterioration of bearing rigidity is restrained.